{Megascleres of the choanosome not differing from those 30. { of the ectosome 31 {Megascleres of the choanosome differing from those { of the ectosome 32 31. {Chelae absent. 33 {Chelae present 44 32. {Trichodragmata present _Tedania_ {Trichodragmata absent 42 {224} [Illustration: FIG. 110.—Megascleres. _a-l_ and _q-s_, Modifications of monaxon type. _a_, Strongyle; _b_, tylote; _c_, oxea; _d_, tylotoxea; _e_, tylostyle; _f_, style; _g_, spined tylostyle; _h_, sagittal triod (a triaxon form derived from monaxon); _j_, oxytylote; _k_, anatriaene; _l_, protriaene; _m_, sterraster (polyaxon); _n_, radial section through the outer part of _m_, showing two actines soldered together by intervening silica; _o_, desma of an Anomocladine Lithistid (polyaxon); _q_, crepidial strongyle, basis of rhabdocrepid Lithistid desma; _r_, young form of rhabdocrepid desma, showing crepidial strongyle coated with successive layers of silica; _s_, rhabdocrepid desma.] {Skeleton reticulate or fibrous{225} 34 33. {Skeleton radiate or diffuse 37 {Skeleton with radiating fibres forming a reticulum with { others crossing them at right angles _Quasillina_ {No microscleres 35 34. {Microscleres sigmata and/or toxa with or without trichodragmata { _Desmacella_ 35. {Sponge fan- or funnel-shaped 36 {Sponge not fan- or funnel-shaped _Hymeniacidon_ 36. {Megascleres slender and twisted _Phakellia_ {Megascleres somewhat stout, not twisted _Tragosia_ 37. {Sigmata present, skeleton diffuse _Biemma_ {Sigmata absent 38 38. {Skeleton more or less radiate 39 {Skeleton diffuse; sponge boring _Cliona_ 39. {Sponge discoid with marginal fringe _Halicnemia_ {Sponge massive or stipitate without marginal fringe 40 40. {Sponge body prolonged into mammiform projections _Polymastia_ {Sponge body without mammiform projections 41